1. Field of the Invention
The present invention relates to a hearing aid having a microphone, a signal processing unit and an earphone, to a method for suppressing electromagnetic disturb signals in a hearing aid of this type.
2. Description of the Prior Art
Signal processing in hearing aids can be impaired by electromagnetic disturb signals, for example by noise fields of mobile telephones. An improvement of the electromagnetic compatibility (EMC) of hearing aids, for example by interconnect optimization and capacitive shielding of microphones, cannot eliminate the noise sensitivity.
European Patent 0 843 427 discloses a system, which uses adaptive comb filters for suppressing periodic electromagnetic disturbance signals. It is necessary to adapt the cutoff frequencies and bandwidths of the comb filter as accurately as possible to the disturbance signal, so that the useful signal is impaired as little as possible.
An object of the invention is to provide a hearing aid and a method, wherein disturbance signals and noise fields are reliably suppressed.
The above object is achieved in accordance with the principles of the present invention in a method for suppressing electromagnetic disturbance signals in a hearing aid, and a hearing aid operating according to the method, wherein a clock element acquires the clock frequency of the disturbance signal that is detected by a detector element in the hearing aid, and the clock element generates a signal and a system clock frequency dependent on the clock frequency of the disturbance signal.
The term xe2x80x9chearing aidxe2x80x9d as used herein refers to separate hearing aids that can be worn at the head or at the body, to hearing aids that can be worn behind the ear, in the ear, to pocket hearing aids and also to hearing aids that can be implanted.
In the inventive hearing aid, it is initially determined via a detector element whether electromagnetic disturbance signals or noise fields are present. If this is the case, a filter element is configured depending on the type of the recognized disturbance signals in order to suppress the noise fields. In this way, the disturbance signals can be filtered out in a way that is adapted to the particular type of the noise field and therefore the filtering is particularly efficient. For example, a comb filter, whose filter characteristic is exactly adapted to the respective disturbance signal, is configured in the filter element. The system clock of the hearing aid can be utilized for configuring the comb filter. Besides, the inventive hearing aid has a clock element for acquiring the clock frequency of the disturbance signal acquired by the detector element. The acquired clock frequency of the disturbance signal is then used for generating the system clock frequency, particularly by frequency multiplication. On the basis of the current clock frequency of the disturbance signal, the system clock frequency is newly generated. The clock frequency of the system clock element of the hearing aid, which is altered or falsified as a result of aging or drift, for example, can be switched off and the newly generated system clock frequency that is derived from the clock frequency of the disturb signal can be used for operating and particularly for configuring the filter element. As a result thereof, a particularly precisely configured filter element is achieved, which is able to suppress the determined disturbance signals in a particularly effective way.
If the clock element has a PLL circuit (xe2x80x9cphase-locked-loopxe2x80x9d), the generated system clock frequency can be generated as a rational multiple of the isolated and acquired disturb signal frequency.
A change element can be connected between the clock element and the system clock element, so that the previous system clock element, after the new system clock frequency has been generated, can be switched off and the hearing aid can be operated for generating a suitable filter characteristic with the newly derived system clock frequency.
In principle, the inventive hearing aid can be digitally or analogously constructed. Given a digital construction, the hearing aid can have a DSP element (digital signal processor element) for a particularly precise signal processing having a number of versions. The filter element for suppressing the disturb signals can be integrated into the DSP element or it can be arranged directly in front of the A-D converter, for example, for particularly effective suppression of the disturbance signals at the end of the signal transmission chain.
After the disturbance signals have been detected, a filter element is inventively configured dependent on the detected disturbance signals for the adapted suppression of the disturbance signals.
The suppression of the disturbance signals is particularly efficient when the clock frequency of the disturbance signal is initially acquired and isolated and when the system clock frequency is subsequently generated particularly by frequency multiplication. As a result of this generated system clock frequency, the filter element can be particularly precisely configured (e.g. high-pass filter, low-pass filter, comb filter, FFT), since the system clock of the hearing aid, that is may be falsified as a result of aging or drift, is not used.
In this version of the inventive method, the disturbance signal itself generates a suitable filtering for suppressing the disturbance signal.
The inventive method is particularly suited for of suppressing electromagnetic disturbance signals of mobile telephones (e.g. according to the GSM standard or DECT standard) and for acquiring the interference characteristics of known mobile radio networks (e.g. D1 network, D2 network, E network, E-plus network).
Electromagnetic noise fields which occur in connection with the network frequency can be detected and suppressed when the hearing aid is operated by means of a telephone coil.
In addition, the detector element can be used for detecting, for example, the ringing or the activation of the mobile telephone due to the arising frequency signals and for making it perceptible directly in the hearing aid.